First test of LOWSPEC.2 Spectrograph

[ejp1684]

I've called it LOWSPEC.2 as it's the updated version of Paul Gerlach's LOWSPEC, a DIY 3D printed spectrograph. I built the first version but had trouble aligning the guide mirror (which was fixed), and locating the slit by waving a torch down the scope made it difficult to use.

The updated version is a vast improvement, for me at any rate.

1. The guide mirror can now be adjusted forward and backwards and side to side. I can now actually guide the spectrograph.

2. Adding an Illumination device (Baader). The slit can now be illuminated and the overlay in PHP2 used to locate it. No more trouble getting the star on the slit.

There is also the option to use a 30mm dia camera lens instead of 24mm. The camera lens used is 100mm focal length; I had a 30mm dia lens left over from a previous diy project which is 90mm focal length so I used that. I'm not sure of its quality as I bought it for £15 from ebay, but it seems to work ok.

I also had a defraction grating of 600 l/mm from a previous project so used that. Paul reckons LOWSPEC will now cope with anything up to a grating of 1800 l/mm.

For calibration I used a Philips S10 starter bulb because I found some calibration charts for it, (I think on one of the French websites) and these bulbs are about £1 in B & Q, significantly less than the Relco ones (if you can get them). I made a hole in the top cover, made a container on the 3D printer and now I simply insert it when I need to get a calibration reading. Not the most practical solution but again, it seems to work. If Paul manages to add a calibration unit inside LOWSPEC, that would be the icing on the cake. And if it could just be attached to the existing body that would be a bonus, as it took me 29 hours to print!

Here's a couple of shots of the thing itself.

The long tube houses the Philips lamp.

Here the calibration unit is inserted into the top cover.

The first reasonably clear night was moonlit and there was high cloud coming and going, but I went first for Vega as it's easy to image and calibrate with the Hydrogen lines.

The salmon coloured line is the A0V reference.

The image of Vega looked quite good on the laptop, so I moved on to P Cygni, one of my favourite subjects, and here are the results.

I've taken some of the readings from a PDF version of Richard Walker's 'Spectroscopic Atlas for Amateur Astronomers'. It doesn't seem to be available for download any more, I think there's now a book which you have to buy.

I may need to get a better guide camera; I'm using an Altair Astro GPCAM mono and when guiding it used a star with a S/N ration of 9.8, the brightest available. But having said that, it managed to keep P Cygni on the slit for 5 minutes at a time.

LOWSPEC is a great project if you've started out using the StarAnalyser and want to move to a higher resolution. It takes a lot of patience and persistence, but worth it. I reckon the total cost for LOWSPEC is about a quarter of the cost of an equivalent 'off the shelf' spectroscope, so if you can't justify spending loads of dosh then this is a viable option.

Eric.

[robin_astro]

Hi Eric,

That's a nice build and first light results.  You can get to impressively high resolution to with the 1800 l/mm grating. There are some recent results with this grating on the VdS forum, for example splitting the binary components of Mizar in the H alpha line

https://forum.vdsastro.de/viewtopic.php?f=24&t=5685

Cheers

Robin

[ejp1684]

Thanks for this, Robin, I'll certainly give it a go as soon as I progress on to using an 1800 l/mm grating.

Eric.

[Thalestris24]

On 17/05/2019 at 20:33, ejp1684 said:

I've called it LOWSPEC.2 as it's the updated version of Paul Gerlach's LOWSPEC, a DIY 3D printed spectrograph. I built the first version but had trouble aligning the guide mirror (which was fixed), and locating the slit by waving a torch down the scope made it difficult to use.

The updated version is a vast improvement, for me at any rate.

1. The guide mirror can now be adjusted forward and backwards and side to side. I can now actually guide the spectrograph.

2. Adding an Illumination device (Baader). The slit can now be illuminated and the overlay in PHP2 used to locate it. No more trouble getting the star on the slit.

There is also the option to use a 30mm dia camera lens instead of 24mm. The camera lens used is 100mm focal length; I had a 30mm dia lens left over from a previous diy project which is 90mm focal length so I used that. I'm not sure of its quality as I bought it for £15 from ebay, but it seems to work ok.

I also had a defraction grating of 600 l/mm from a previous project so used that. Paul reckons LOWSPEC will now cope with anything up to a grating of 1800 l/mm.

For calibration I used a Philips S10 starter bulb because I found some calibration charts for it, (I think on one of the French websites) and these bulbs are about £1 in B & Q, significantly less than the Relco ones (if you can get them). I made a hole in the top cover, made a container on the 3D printer and now I simply insert it when I need to get a calibration reading. Not the most practical solution but again, it seems to work. If Paul manages to add a calibration unit inside LOWSPEC, that would be the icing on the cake. And if it could just be attached to the existing body that would be a bonus, as it took me 29 hours to print!

Here's a couple of shots of the thing itself.

The long tube houses the Philips lamp.

Here the calibration unit is inserted into the top cover.

The first reasonably clear night was moonlit and there was high cloud coming and going, but I went first for Vega as it's easy to image and calibrate with the Hydrogen lines.

The salmon coloured line is the A0V reference.

The image of Vega looked quite good on the laptop, so I moved on to P Cygni, one of my favourite subjects, and here are the results.

I've taken some of the readings from a PDF version of Richard Walker's 'Spectroscopic Atlas for Amateur Astronomers'. It doesn't seem to be available for download any more, I think there's now a book which you have to buy.

I may need to get a better guide camera; I'm using an Altair Astro GPCAM mono and when guiding it used a star with a S/N ration of 9.8, the brightest available. But having said that, it managed to keep P Cygni on the slit for 5 minutes at a time.

LOWSPEC is a great project if you've started out using the StarAnalyser and want to move to a higher resolution. It takes a lot of patience and persistence, but worth it. I reckon the total cost for LOWSPEC is about a quarter of the cost of an equivalent 'off the shelf' spectroscope, so if you can't justify spending loads of dosh then this is a viable option.

Eric.

Hi Eric

I was thinking of doing something similar re the calibration lamp. I was wondering whether your S10 bulb was poking down towards the front of the slit or whether you had some sort of reflector within the holder. It would seem good to have the S10 more or less permanently in place but not otherwise interfering in the light path to the slit. Oh, I see you only insert yours when you want to make a calibration.

Season's greetings!

Thanks

Louise

[Merlin66]

Eric,

Well done mate!

Looks like you're of to a good start.

 

[Merlin66]

Eric,

Re-reading your post...

What were/ are your issues with the reflective slit acquisition and guiding? Do you have a guide image to share?

Many of us now use the OVIO slitplate for guiding with few if any issues. Why do you think the illuminator is worthwhile fitting?

What slit gap did you use?

Edited December 26, 2019 by Merlin66

[ejp1684]

The issues I had with the guiding were to do with the first version of Lowspec where the guide mirror was fixed in position and not easy to adjust. In this latest version the guide mirror is adjustable and I found it easy to get the slit in the centre of the camera.

In my setup the slit is not easy to see at night ( I think I need a more sensitive camera), so having the illuminator fitted allows me to quickly check where the slit is, and to set the slit overlay onto it (using PHD2).

I'm using the 20 micron slit.

Eric.